Most studies of lung function have been carried out with either whole lung or lung slices. Because lung contains at least 40 different types of cells, such studies are difficult to interpret. Clearly preparations are needed that are predominantly of one single cell type. However, as a first step, studies with preparations consisting of mixed population of lung cells are needed to evaluate various techniques for separating and isolating functional cell types. Our initial studies on the effect of cholinergic agents on cyclic nucleotide levels in lung cells were carried out on viable lung cells prepared by proteolysis of the lung tissue according to the method of Gould et al. (Science 178:1209, 1972).